1. Field
The disclosed technology relates to micro-optical metal transmission grating technology, and particularly to a sub-wavelength extreme ultraviolet metal transmission grating and manufacturing method thereof.
2. Description of the Related Technology
Transmission gratings are widely used as high-resolution chromatic dispersion optical elements due to advantages of simple structure, wide optical spectrum, smooth energy response, and flat spectrum surface, etc. The transmission gratings can be combined conveniently with temporal or spatial analysis equipments to constitute measurement systems capable of diagnosing temporal and spatial energy spectrum characteristics of plasma simultaneously. As a result, the transmission gratings have extensive usage in astrophysics and inertia-constraint nuclear fusion. Sub-wavelength metal transmission gratings as one kind of the transmission gratings play an important role in the aforementioned applications.
Diffraction and diffusion may occur when light wave is incident on a surface of a metal film having periodically-arranged sub-wavelength apertures, generating a transient field at the surface of the metal film. The transient field is effectively amplified at the incident surface by plasmon near-field enhancement effect and then transmitted to an exit surface through the sub-wavelength apertures. The transient field is amplified again at the exit surface by the plasmon near-field enhancement effect, resulting in far-field enhancement effect. This phenomenon is called ultra-strong transmission. Accordingly, metal transmission gratings having a period in a wavelength order as a simplified model of micro-nano structures of metal have been proposed as a basic structure for studying interaction between light and periodic metal structures. It has been proved theoretically that the transmission enchantment effect also exists for the metal transmission gratings. However, diffraction efficiency is extremely low for metal transmission gratings in the extreme ultraviolet waveband. Thus, it is meaningful if the transmission enchantment effect can be applied to the metal transmission gratings in the extreme ultraviolet waveband.
However, current study of the sub-wavelength metal transmission gratings mainly focuses on visible waveband and near-infrared waveband. Such metal gratings have a relatively large period and thus are simple in structure and easy for manufacture and analysis. For the extreme ultraviolet waveband, however, the metal transmission gratings need to have a period near or even less than the wavelength and a duty cycle of 1:1. It is very difficult to manufacture such metal transmission gratings. When resist patterns are written directly using an electron beam, the resist is prone to collapse due to proximity effect and back-scattering. Moreover, it is difficult to obtain a desired thickness of the resist, thereby limiting an aspect ratio of the metal grating. This becomes an obstacle in implementing desirable phase and amplitude modulation of light.
In order to address the various problems in the prior art, the disclosed technology provides a sub-wavelength extreme ultraviolet metal transmission grating and manufacturing method thereof.